5-Bromo-2-fluorobenzeneboronic acid is an important intermediate in the synthesis of a number of non-ester pyrethroid compounds. 5-Bromo-2-fluorobenzeneboronic acid and processes for its preparation are described in U.S. Pat. No. 5,068,403 and Pesticide Science, 28, pp. 25-34 (1990), which are incorporated herein by reference. Those references disclose that 5-bromo-2-fluorobenzeneboronic acid is prepared from 2,4-dibromofluorobenzene. However, 2,4-dibromofluorobenzene is not entirely satisfactory for use in the commercial manufacture of 5-bromo-2-fluorobenzeneboronic acid.
2,4-Dibromofluorobenzene is commercially available as a mixture containing seventy percent 2,4-dibromofluorobenzene and thirty percent 3,4-dibromofluorobenzene. When that mixture is used to prepare 5-bromo-2-fluorobenzeneboronic acid, at most, only a 70% yield is obtainable based on the total amount used. In addition, to obtain high purity 5-bromo-2-fluorobenzeneboronic acid, a time-consuming purification step is required to remove impurities such as 3,4-dibromofluorobenzene. A process that avoids the use of 2,4-dibromofluorobenzene would provide a great improvement over the art processes.
It is therefore an object of the present invention to provide a process for the preparation of 5-bromo-2-fluorobenzeneboronic acid which avoids the use of 2,4-dibromofluorobenzene.
The present invention provides a process for the preparation of 5-bromo-2-fluorobenzeneboronic acid which comprises lithiating 1-bromo-4-fluorobenzene with a lithium base in the presence of a solvent to form (5-bromo-2-fluorophenyl)lithium, reacting (5-bromo-2-fluorophenyl)lithium with a tri(C.sub.1 -C.sub.6 alkyl) borate to form a di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate, and hydrolyzing the di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate. It has been found that the process of this invention is more effective and efficient than the prior art processes, and avoids the use of 2,4-dibromofluorobenzene which is commercially availably only as an impure mixture.
The present invention also provides a process for the preparation of a fluoroolefin compound of formula I ##STR1## wherein Ar is phenyl optionally substituted with any combination of from one to three halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 haloalkyl, C.sub.1 -C.sub.4 alkoxy or C.sub.1 -C.sub.4 haloalkoxy groups, or
1- or 2-naphthyl optionally substituted with any combination of from one to three halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 haloalkyl, C.sub.1 -C.sub.4 alkoxy or C.sub.1 -C.sub.4 haloalkoxy groups;
R is hydrogen and R.sub.1 is cyclopropyl, or R and R.sub.1 are each independently C.sub.1 -C.sub.4 alkyl, or R and R.sub.1 are taken together with the carbon atom to which they are attached to form a cyclopropyl group. PA1 lithiating 1-bromo-4-fluorobenzene with a lithium base in the presence of a solvent to form (5-bromo-2-fluorophenyl)lithium, PA1 first reacting (5-bromo-2-fluorophenyl)lithium with a tri(C.sub.1 -C.sub.6 alkyl) borate to form a di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate, PA1 hydrolyzing the di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate to form 5-bromo-2-fluorobenzeneboronic acid, PA1 oxidizing 5-bromo-2-fluorobenzeneboronic acid to form 5-bromo-2-fluorophenol, PA1 second reacting 5-bromo-2-fluorophenol with bromobenzene and a base to form 5-bromo-2-fluorophenyl ether, PA1 third reacting 5-bromo-2-fluorophenyl phenyl ether with magnesium to form the corresponding magnesium bromide, and PA1 fourth reacting the magnesium bromide with a compound having the formula ##STR3## wherein Ar, R and R.sub.1 are as described above and Q is OC(O)CH.sub.3 or Br in the presence of a transition metal catalyst.
The configuration of the hydrogen atom and the fluorine atom about the double bond is mutually trans. The process comprises lithiating 1-bromo-4-fluorobenzene with a lithium base in the presence of a solvent to form (5-bromo-2-fluorophenyl)lithium, reacting (5-bromo-2-fluorophenyl)lithium with a tri(C.sub.1 -C.sub.6 alkyl) borate to form a di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate, hydrolyzing the di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate to form 5-bromo-2-fluorobenzeneboronic acid, oxidizing 5-bromo-2-fluorobenzeneboronic acid to form 5-bromo-2-fluorophenol, reacting 5-bromo-2-fluorophenol with bromobenzene and a base such as sodium hydride to form 5-bromo-2-fluorophenyl ether, reacting 5-bromo-2-fluorophenyl ether with magnesium, and reacting the resulting compound in the presence of a transition metal catalyst such as a cuprous halide, cuprous cyanide or Li.sub.2 CuCl.sub.4 to form the desired fluoroolefin of formula I. The fluoroolefin compound is useful in a pesticide composition.
Compounds of Formula I may have a trans or cis configuration of the hydrogen and fluorine atom about the double bond. Compounds having a trans configuration are preferred, and are prepared by using the reactant III (as described below) having a trans configuration. To prepare compounds of Formula I with a cis configuration, a reactant III having a cis configuration is used. To prepare compounds of Formula I having a mixture of trans and cis configurations, a reactant III having a mixture of trans and cis configurations is used.
The invention is described in the following specific embodiments:
1. A process for preparing 5-bromo-2-fluorobenzeneboronic acid, the process comprises lithiating 1-bromo-4-fluorobenzene to form (5-bromo-2-fluorophenyl)lithium; reacting (5-bromo-2-fluorophenyl)lithium with a tri(C.sub.1 -C.sub.6 alkyl) borate to form a di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate; and hydrolyzing the di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate.
2. The process of embodiment 1 wherein the lithiating step is at a temperature of less than about 0.degree. C.
3. The process of embodiment 2 wherein the temperature is less than about -40.degree. C.
4. The process of embodiment 1 wherein the 1-bromo-4-fluorobenzene in the lithiating step is reacted with a lithium base.
5. The process of embodiment 4 wherein the lithium base is a lithium dialkylamide or a lithium cyclic amide.
6. The process of embodiment 4 wherein the 1-bromo-4-fluorobenzene in the lithiating step is reacted with the base in the presence of a solvent.
7. The process of embodiment 6 wherein the solvent is an ether.
8. The process of embodiment 1 wherein the tri(C.sub.1 -C.sub.6 alkyl) borate is trimethyl borate.
9. The process of embodiment 1 wherein the di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate is hydrolyzed with an organic or mineral acid.
10. The process of embodiment 9 wherein the organic or mineral acid is an aqueous acid.
11. A process for the preparation 5-bromo-2-fluorobenzeneboronic acid which comprises lithiating 1-bromo-4-fluorobenzene with a lithium base in the presence of a solvent to form (5-bromo-2-fluorophenyl)lithium, reacting (5-bromo-2-fluorophenyl)lithium with tri(C.sub.1 -C.sub.6 alkyl) borate to form a di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate, and hydrolyzing the di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate.
12. The process according to embodiment 11 wherein 1-bromo-4-fluorobenzene is lithiated with the lithium base at a temperature below about 0.degree. C.
13. The process according to embodiment 12 wherein the temperature is below about -40.degree. C.
14. The process according to embodiment 11 wherein the lithium base is a lithium dialkylamide or a lithium cyclic amide.
15. The process according to embodiment 14 wherein the lithium base is lithium diisopropyl amide.
16. The process according to embodiment 11 wherein the solvent is an ether.
17. The process according to embodiment 16 wherein the ether is tetrahydrofuran.
18. The process according to embodiment 11 wherein the tri(C.sub.1 -C.sub.6 alkyl) borate is trimethyl borate.
19. The process according to embodiment 11 wherein the di (C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate is hydrolyzed with an aqueous organic acid or an aqueous mineral acid.
20. A process for the preparation 5-bromo-2-fluorobenzeneboronic acid which comprises lithiating 1-bromo-4-fluorobenzene with a lithium base selected from the group consisting of a lithium dialkylamide and a lithium cyclic amide in the presence of an ether to form (5-bromo-2-fluorophenyl) lithium with a tri(C.sub.1 -C.sub.6 alkyl) borate to form a di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate, and hydrolyzing the di(C.sub.1 -C.sub.6 alkyl) 5-bromo-2-fluorobenzeneboronate with an aqueous organic or mineral acid.
21. A process for preparing a fluoroolefin compound having the formla ##STR2## wherein Ar is phenyl optionally substituted with any combination of from one to three halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 haloalkyl, C.sub.1 -C.sub.4 alkoxy or C.sub.1 -C.sub.4 haloalkoxy groups, or 1- or 2-naphthyl optionally substituted with any combination of from one to three halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 haloalkyl, C.sub.1 -C.sub.4 alkoxy or C.sub.1 -C.sub.4 haloalkoxy groups; R is hydrogen and R.sub.1 is cyclopropyl, or R and R.sub.1 are each independently C.sub.1 -C.sub.4 alkyl, or R and R.sub.1 are taken together with the carbon atom to which they are attached to form a cyclopropyl group; and the configuration of the hydrogen atom and the fluorine atom about the double bond is mutually trans. The process comprises
22. The process of embodiment 21 wherein the base in the second reacting step is sodium hydride.